Présentations Colloques

Oral Presentation
Session 2.02: Groundwater for sustainable water supplies in developing countries
Abera Fenta Nigate
Hydrologic interconection between then Volcanic Aquifer and Springs, Lake Tana Basin on the Upper Blue Nile
This research wants to find out whether the high discharge springs around Bahir Dar in Lake Tana Basin are locally or regionally recharged. Water samples from boreholes and springs were collected and analyzed and compared for major cations and anions. Hydrochemical and stable isotope (sigma18O and sigma2H) data were used to identify the recharge sources of major springs and the hydraulic interconnection between the volcanic aquifer and springs in the Gilgel Abay catchment and adjacent areas. The hydrochemical data analysis showed that all water samples of springs and shallow wells have freshwater chemistry, Ca-HCO3 to Ca-Mg-HCO3 types. This is mainly controlled by dissolution hydrolysis of silicate minerals. The analyzed stable isotope data indicate that springs water, except Dengel Mesk, Kurt Bahir and Bility springs, and well waters, except Dangila well, fall close to the LMWL. This clearly shows that the infiltrated rainwater did not undergo much evaporation and sigma 18O values for spring water and groundwater are nearly equal to the value of Ethiopian summer rainfall, which is -2.5‰. Therefore, generally both stable isotope and hydrochemical data show the recharge source to springs and shallow groundwater is primarily from precipitation. Furthermore, data suggest that rock-water interaction has remained relatively limited, pointing to relatively short residence times, and local recharge rather than regional recharge.